This study, using data from the NINCDS Collaborative Perinatal Project, investigates the relation of selected factors which may affect the mothers during pregnancy, and possibly cause congenital heart defects in the children. Observations on about 47,000 pregnancy records provide case and control data for analysis. Some 486 children have been identified as having definite congenital cardiac anomalies. These include cardiac conditions which are part of known syndromes but exclude children suspected of having ventricular septal defect who are reported without cardiac defect at the 1-year examination and thereafter. Pre-selected maternal risk factors noted in the pregnancy records for the mothers of 392 children with definitely defined congenital heart anomalies are compared with control data matched for maternal age, race, date of LMP, and geographical location (institution).